In conventional image forming device and like devices, a fixing process is carried out for fixing toner onto a recording material. In the fixing process, a toner image formed with toner or the like on the recording material in an image forming process in an upstream of the fixing process is heated so that the toner is melted and fixed onto the material, while the recording material is being transported between two cylindrical members, namely a fix member and a press member.
The fix member, if thinner than the conventional fix member, may require a longer warm-up time (may have a poor warm-up performance), depending on the balance of the heating and adiabatic performance of the fix and press members between which the recording material is transferred. The extension of warm-up time will reduce convenience. Adverse effects are not limited to the warm-up time extension; the warm-up time extension results in higher power consumption level in standby mode, against the popular trend of energy conservation.
A common approach available to energy loss reduction is to improve the thermal insulation of the whole fixing device. However, if the balance of the heating and thermal insulating (adiabatic) performance of the fix and press members is anything less than desirable, the device consumes more power in the heating of the recording material for the fixing, thereby adversely affecting the overall energy saving performance by the image forming device.
The warm-up performance especially affects power consumption in warm-up and standby, as well as convenience in use. In some cases, regulations were or will be set to set higher standards for the warm-up performance. Further, the power available for the image forming device to perform the heating and fixing of the recording material are so limited. In some cases, the image forming device would be undesirably underpowered depending on various power supply conditions, such as a number of periphery devices added, countries or regions the image forming device is used, etc. It is desired that the image forming device is capable of performing the fixing on less electric power.
In view of the aforementioned problems, Japanese patent 2994858 (registered on Dec. 27, 1999), conventional art, discloses a fixing device in which the fix member has a lowered thermal capacity and the press member is made of silicone sponge. The silicone sponge has fine air bubbles in it for improved thermal insulation. The air bubbles gives the silicone sponge higher heat insulating (adiabatic) property.
The use of silicone sponge press member works well when the press and fix members are under a light load. It however faces structural problems of the silicone sponge press member itself and the fix member, when applied to high speed, heavy load conditions.
For example, to perform high speed printing at a high throughput, the nip needs be wider so that it can provide heat to the toner and recording material quickly. One could readily achieve a wider nip by making the press member from a softer silicone sponge material. This however would make the air bubbles in the silicone sponge easy to collapse, thereby leading to permanent deformation of the silicone sponge, depriving the required level of elasticity from the silicone sponge.
In an arrangement where low temperature fixing is adopted for alleviating the adverse effects of high temperature on the recording material and the toner, the permanent deformation of the silicone sponge, and the resultant loss of elasticity in the silicone sponge would also be caused when the air bubbles in the silicone sponge, as described above, becomes easy to collapse as the result of the application of a heavy load to the fix and press members for high speed printing. The silicone sponge or like elastic body could permanently deformed markedly at near a surface thereof, thereby leading to lower thermal adiabatic performance of the press member. This would result in the nip with too large width, and thus excessive fixing. The excessive fixing leads to inconveniences like high temperature offset and twining. When the permanent deformation of the press member is further progressed, the press member cannot sustains its elasticity by which it can function as it is. Such loss of elasticity shortens life of the press member and the device to which the press member is provided.
As described above, the use of silicone sponge for the press member is associated with the various problems in order to deal with the high speed and heavy load, thus it is difficult to realize high-speed printing by the use of silicone sponge for the press member.